Hot forming behavior of a modified Ni–Cr superalloy

The hot working behavior of a 38Ni-21Cr based superalloy was studied. Torsion tests at strain rates between 2 and 20 s${}^{-1}$ and temperatures between 1 123 and 1 473 K were conducted. A fine microstructure of about 6–10 μm grain size and small TiC particles were observed after torsion tests at 1 473 K and 4 s${}^{-1}$. The results of these tests were analyzed using MATLAB and MS EXCEL programs to obtain the parameters of the Garofalo equation able to correlate the experimental data with a single equation. Stress exponent values much higher than 5 and a high activation energy for deformation suggest that the deformation is controlled by a slip creep mechanism characteristic of reinforced materials. The optimum forming temperatures at different strain rates were determined by means of the second Lyapunov stability equation. An optimum stability temperature of 1 643 K (1 370 °C) at 10 s${}^{-1}$ is determined.